Indian Phytopath. 63 (2) : 174-180 (2010) Adult plant resistance in some Indian wheat genotypes and postulation of leaf rust resistance genes S.C. BHARDWAJ*, M. PRASHAR, S.K. JAIN, SUBODH KUMAR and D. DATTA 1 Regional Station, Directorate of Wheat Research, Flowerdale, Shimla 171 002 1 Indian Vegetable Research Institute, Varanasi 221 305 ABSTRACT: Advanced breeding lines and released/identified varieties of wheat were screened against different pathotypes of Puccinia triticina for leaf rust resistance both at seedling as well as adult plant stage in controlled polythene house conditions. Different combinations of seven resistance genes, viz. Lr1, Lr3, Lr10, Lr13, Lr23, Lr26 and Lr34 were characterized by applying the gene matching technique in 39 wheat lines that showed race-specific adult plant resistance (APR) to one and/or the other pathotypes. APR of both hypersensitive and non-hypersensitive types was observed. Varieties GW 322 (Lr13+) and NIAW 34 (Lr13+34+) showed APR to the three most pathogenic and virulent pathotypes 1R5 (12-2), 121R63-1(77-5) and 21R55(104-2). Twenty-one wheat lines/varieties showed APR to only two pathotypes. The remaining 16 lines showed APR to only one of the three pathotypes. Such race-specific adult plant resistance would be useful in breeding for leaf rust resistance. The seedling and adult plant resistance of these lines can be useful in increasing genetic diversity and avoiding leaf rust epiphytotics on wheat. Key words: Leaf (brown) rust, Puccinia triticina, wheat, seedling resistance, and adult plant resistance Rusts are the most important diseases of wheat worldwide. Of the three wheat rusts (leaf, stem and stripe), leaf (brown) caused by the fungus Puccinia triticina Eriks., is the most damaging . In India, the disease is found in all wheat-growing areas (Bhardwaj et al., 2006) and its capability to spread under Indian conditions is well documented. The ability of the fungus to mutate, multiply rapidly, and spread over large areas has led to widespread epiphytotics in India (Nagarajan and Joshi, 1975). The detection of pathotypes and characterization of rust resistance genes in wheat lines are carried out regularly and the resulting information is used for managing leaf rust. Among the different methods of disease control, host resistance is the most economic and environment friendly method of reducing yield losses caused by leaf rust. Resistance that contains catalogued Lr genes is quite useful for managing leaf rust of wheat. However, a shift in virulence and the emergence of new pathotypes may render the resistant Lr genes susceptible, generally due to their race- specific nature (McIntosh et al., 1998). The leaf-rust resistant APR genes, Lr12, Lr13, Lr22a and Lr22b, showed race specificity in their response to rusts throughout the world and also in many Indian wheat varieties (Dyck and Kerber, 1985; Kolmer, 2003; Nayar et al., 2005). The resistance of known APR gene Lr34 in North America has been termed non-race specific. The APR genes Lr12, Lr13 and/or Lr34 present in many wheat lines appear to be derived from either Chinese Spring or Frontana cultivars (Kolmer, 1996). In the study reported herein, advance wheat lines and varieties were evaluated for resistance against leaf rust at the seedling and adult plant stages, in order to identify resistant at these two stages. MATERIALS AND METHODS Wheat material The seedlings and adult plants of 343 advance wheat lines and varieties were evaluated for resistance to different pathotypes of Puccinia triticina during 2003-06 at Flowerdale. These included both durum and bread wheat varieties, many of which were released for cultivation in different agro-ecological wheat growing areas of India. Pathotypes used Sixteen pathotypes of P. triticina were used for the seedling resistance studies, while only three pathotypes, i.e. those that were considered the most virulent and predominant, were used to evaluate APR. For the understanding of worldwide wheat community, the international equivalents of these pathotypes are given in Table 2, following McVey et al. (2004). The avirulence/virulence formulae of the three pathotypes used in APR studies are detailed in Table 1. Growing of seedlings and inoculation The seedlings were grown in aluminium bread pan trays (29cm longx12cm wide x7 cm deep size) in a mixture of fine loam and farmyard manure (3:1) that had been sterilized by autoclaving (60 0 C) for one hour. For each wheat line, about 5-6 seeds were sown. Proper checks, including lines with known genes or near isogenic lines (NILs) with APR effect and known Lr genes in Indian wheat were also evaluated. The seedlings were raised in spore-proof greenhouse chambers at 22 +2 0 C, 50-70% relative humidity and 12-hour daylight. When the seedlings were one week old with fully expanded primary leaves, they were inoculated using a *Corresponding author: scbfdl@hotmail.com